The EP process includes a laser discharging a charged PC drum to create a latent image that becomes toned with one or more toners (e.g., black, cyan, magenta, yellow). A voltage difference between the drum and an opposed transfer roll transfers the image to a media sheet or to an intermediate transfer member (ITM) for subsequent transfer to a media sheet. A corona or charge roll sets the charge on the PC drum and a developer roll introduces the toner to the latent image. A controller coordinates with one or more high voltage power supplies to provide power to the laser and to set relevant charges on the rolls. As is known, the control of the surface voltage potential on the PC drum is highly critical to a well-performing EP process, not only for image development, but also for minimizing waste toner.
However, it has been observed in many imaging devices that, with aging components, variability increases, especially for charge rolls. It occurs for many reasons but includes variation in the wear rates of the rolls and influences from environmental conditions, the nature of a customer run mode, and the composition of the rolls. The ability to compensate for each of these variables independently using crude open loop adjustments can be extremely difficult. Therefore, a need exists to accurately detect, and compensate, the PC surface voltage dynamically throughout the life of a machine. The inventors note this type of detection would then allow the imaging device to apply a proper charge compensation and prevent unwanted background/waste toner development when the charge levels drift above or below desired set points.
As has also been observed, charge voltage compensation in imaging devices is often performed through one or more of the following options: (1) using a set of preconditions and open loop modifications derived from empirical test data; (2) adding circuitry to the high voltage power supply to provide direct current feedback of the charge roller; (3) using an optical density sensor to detect unwanted background toner; (4) using a weather station to compensate for environmental conditions; and (5) using an electrostatic probe as precise feedback to known the surface potential of the drum. Although the first option provides less expense for an imaging device, it likely results in higher amounts of variation. The latter four options, however, can provide the most direct feedback for proper compensation, but for more economical imaging devices they are costly additions to the bill of materials. A need exists to overcome these and other problems.